It is the central hypothesis of this proposal that an effective strategy can be developed to treat metastatic colorectal carcinoma in the liver with in vivo adenovirus (Ad) vector-mediated "regional" prodrug therapy. The proposal focuses on the Ad vector-mediated transfer of the prokaryotic cytosine deaminase (CD) gene directly to normal hepatocytes and systemic administration of 5-fluorocytosine (5FC). The hepatocytes convert the 5FC to the active chemotherapeutic agent 5-fluorouracil (5FU), which will diffuse locally and suppress the growth of the metastatic tumor cells, while not harming the normal cells which catabolize the 5FU. The preliminary evidence indicates that intravenous administration of the Ad vector will work,obviating the need for cumbersome, expensive target strategies. While this strategy may appear counter-intuitive, and opposite to the popular strategy of tumor-specific vector targeting and/or tumor- specific expression of therapeutic genes, the preliminary data suggest this will be effective, and without significant toxicity. Xenogeneic and syngeneic models of colorectal metastases to liver will be used to rigorously demonstrate that hepatocyte-directed Ad-mediated CD transfer will convert systemically administered 5FC to sufficient amounts of 5FU to effectively suppress the growth of the tumor cells, without significant toxicity. To maximize the control over the CD gene that is transferred to hepatocytes via the AD vector, chimeric promoters will be designed to permit up-regulation of expression of the CD gene and hepatocyte-specific expression. Finally, Ad vectors will be constructed that will have a different exterior, to escape recognition by anti-Ad neutralizing antibodies, permitting repetitive administration.